Flash finally raised my curiousity by adding fully programmable audio in Flash player 10. This means you can read the currently playing audio stream to provide reasonably accurate VU meters etc, but more interesting, it means you can write your own audio-generating algorithms.
To test if flash is actually fast enough and to see if it’s really possible to write flash apps using nothing but the free mxmlc compiler and emacs, I wrote a simple synthesizer in flash 10. The result is fairly pleasing.